Allyl ( 3 -C 3 H 5 ), a four-electron donor, was used as a ligand model to replace 5 -C 5 Me 4 SiMe 3 in DFT calculations on the tetranuclear yttrium polyhydrido complex ( 5 -C 5 Me 4 SiMe 3 ) 4 Y 4 H 8 containing a Y 4 H 8 tetrahedral core structure, which may separate the four -allyl groups and hence suppress the allyl ligand coupling during the computation. In terms of the calculated core geometry, isomerization energy barrier, charge population, and frontier orbital features of the complex, the 3 -C 3 H 5 ligand model is comparable to 5 -C 5 H 5 .